


ok.

by syzygykitty



Category: Undertale (Video Game)
Genre: Aftercare, Alternate Universe - Underfell, BDSM, Bath Sex, Biting, Bondage, Choking, Collars, Cunnilingus, D/s relationship, Daddy Kink, Degradation, Dirty Talk, Dom!Sans, Established Relationship, Explicit Sexual Content, Fluff, Fluff and Smut, Gentle Sex, Growling, Masochism, NSFW, Other, Painplay, Pet Names, Reader has a vagina, Reader has no defined gender, Reader-Insert, Smut, Underfell Sans, Underfell!Sans - Freeform, like a lot of aftercare
Language: English
Status: Completed
Published: 2016-10-04
Updated: 2016-10-13
Packaged: 2018-08-19 13:21:41
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 4,394
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/8210063
Author URL: https://archiveofourown.org/users/syzygykitty/pseuds/syzygykitty
Summary: You've known each other for a long time, and loved each other nearly as long. But there are times when you still need to remind each other that you're not going anywhere.(Please note the tags. Although chapter 1 is SFW, Reader and Sans are in a D/s relationship in which Reader is the sub and wears a collar. Chapter 2 is NSFW.)





	1. Chapter 1

**Author's Note:**

> This fic was originally inspired by [this picture](https://kierie.tumblr.com/post/150806237730/everybodys-favorite-sweaty-asshole-hes), drawn by the incredible kierie on tumblr. (Please note that the picture is SFW, but the tumblr itself is not!) Thank you very much to kierie for allowing me to use your art as inspiration!
> 
> However, I may have... totally run away with the idea, and the fic ended up bearing very little resemblance to either kierie's version of UF!Sans or the original picture itself. Whoops.
> 
> This is the first writing I've done in years, fic or not, and I get the feeling that this is total crap. Oh well. I wrote it to make myself feel better, and it did.
> 
> (Edit: Thank you so much for 200 kudos! <3)

You sit there, on the floor, leaned comfortably against his legs. He’s reading the physics book he bought yesterday at your encouragement. You’re glad he bought it. He’s so focused now, not that he isn’t focused most of the time. It’s just… nice, for once, to see him immersed in something he loves, something he wants to concentrate on, rather than tearing himself apart trying to protect everyone all at once, trying to anticipate everything that could possibly go wrong. Trying to keep his grin natural, his demeanor unaffected and smooth, his jokes easy.

You feel your soul flinch at the memories, all-too-easy to call up, of his strained grin, of the grin he has when he’s doing his damndest not to worry you, and you turn your face into him and put your hand on his foot. He doesn’t look away from the book, but his hand comes down to run through your hair and along the smooth chain of your collar. You relax at that, at the feeling of his phalanges skimming across the back of your neck, at the gentle pull of the silver chain and the reminder that you belong to each other. You push yourself back into his hand, wanting to feel it again, stronger, not just for the security it brings you, but him too.

He looks up from his book now, or rather down to look at you on the floor, and takes his glasses off. You’re almost sorry about that – it had taken him so long to even admit he needed them when he read, much less work up the nerve to ask Alphys for glasses that would stay on his skull without any visible support. And he looks adorable in them, which is a plus. 

He pulls you from your thoughts by asking you, “ya doin’ ok, kitten?” You nod immediately, and when he looks dissatisfied with that, say, “Yes, I’m fine. I just love you.” 

Even now, after so long, he still flushes a little at that, his crimson pupils flaring and fangs parting as he breathes in and more sweat beads on his brow. He knows you mean it, of course he does, but it still thrills him a little every time you tell him. You don’t have to ask him to know that. You can see it, on his face, and you can feel it, in your soul, bonded to his forever.

He puts his book aside and pats his lap. You comply and climb onto him, ignoring the hardness of his femurs. There was a time when that hardness frightened you, but you’ve come to accept it, love it as just another part of him. You hook your fingers in his ribs through his t-shirt and lean gratefully on him, curling up your legs and breathing him in, trying to hold the unpleasant memories back. He tucks his broad arms around you, holding you to him with a grip you know will never falter or fade. He brushes your hair out of your face and puts his fingers under your chin to make you look into his eyes, looking skeptical.

“baby. don’t lie ta me.” You almost close your eyes and turn away in shame at that, but catch yourself at the last moment and keep looking at him, wanting to explain but feeling the words stuck in your throat.

It’s no use, you know. He can feel your soul twisting with uncertainty and sadness just as surely as you can feel his soul roiling with protectiveness and frustration, reaching out to you. You find your eyes filling with tears suddenly and bring your hands up from his ribcage to brush them away before they can even fall.

He looks both angry and frantic now, and he pulls your hands away from your face and swipes roughly at your cheeks. “oh, shit, kitten, c’mon. don’t leave me bone dry here, tell me what’s up.”

You huff out a little laugh despite yourself. “’M sorry,” you tell him, and smile up at him even though you’re really crying now. “I was just thinking about… how long we’ve been together. And how hard you work to protect everyone, and keep us happy. I just, uh, I just want you to be happy too.” He seems almost indignant at that and you smile again through your tears and cut him off before he can protest, “I know, you are happy. You tell me all the time. I just… still. I can’t help but worry about it, sometimes.”

He gathers you closer and kisses you the best he can, sharp teeth, lipless and all, still holding onto your chin. You close your eyes and kiss him back forcefully, caressing the sides of his skull and opening your mouth. He plays at your tongue with his own for a moment, knowing how much both you and he need closeness in moments like these, but pulls back after a few seconds, smiling a little more at your quiet whine.

“i love ya, kitten,” he tells you, and pulls at your collar for real this time, catching the clasp in his hand and stroking it with his thumb. “an’ ya know how happy ya make me. never been happier. jes’ cuz it’s my job ta protect my family don’t mean ‘m not happy.” He pulls his eyes from your collar, back up to you, searching your eyes. “doll… ya know how much i need ya. i don’t gotta remind ya of that, ya remember how i was when we met. bein’ able to keep ya safe an’ with me… thaz the best thing i coulda asked for.”

And the thing is, you know it’s true. You remember the Sans you met for the first time, years ago, in the snow under a mountain. That Sans could never have held you in his arms like this, kissed you gently, kept you next to him without fear. The Sans who lived Underground was broken in a way that both of you are still working to fix.

You watch his eyes, and he looks back at you for a few seconds before his face flushes and he ducks his head, making you laugh softly. It still surprises you, how bashful he is when it comes down to it, even though most of the time, he appears to be perfectly in control. So you take advantage of his momentary embarrassment and put your hands on his face, making him look at you again. “C’mon, Sans. Let’s go up to bed.”

He searches your eyes one more time, and seems happy with what he finds there.

It’s not even eight PM. But he scoops you up in his arms and kisses your cheek and says, “ok.”


	2. Chapter 2

**Notes for the Chapter:**

> Yeah, this might actually be more aftercare than it is smut. But the aftercare is smutty, if that makes up for it...?

“which one ya wearin’ tonight, babe?” he asks you as he carries you up the stairs to your shared bedroom.

“The blue one,” you say confidently, and he grins a little wider and chuckles, “knew it.”

When he sets you on the bed and turns to get the blue leather collar you only wear when you want him to be rough with you, you assume a position you know he loves to see you in: kneeling, hands on your knees, head titled back slightly so he can see your neck. It works – when he turns back and finds you waiting for him like that, he stops short and growls a little, under his breath, phalanges tightening on the dully spiked loop of leather he holds in his hands. You can see him holding himself back as he approaches you, a thrill running through your veins at the power you hold over him, even as you are so totally subservient.

You watch him as he reaches around to the back of your neck and removes the silver collar with one easy motion. He’s trembling slightly, fumbling for the other collar. “ya remember yer safeword?” he asks once he finally has it, fastening the clasp.

“Red,” you tell him immediately. He asks every time. You’ve only had to use it once or twice, but it makes him feel more secure to hear it from you at the beginning of every scene.

“thaz right,” he says, and then his grin widens and his eyes flare a little brighter, “now stay still, babydoll. i gotta rip those fuckin’ clothes off yer pretty lil’ body.” – but he sees the look in your eyes, a silent plea not to destroy your comfiest pajamas, and relents, pulling them off you gently instead of ripping them. He tosses them off the bed and crawls over you, leaning down to kiss you as he covers your body with his own. You arch up against him, hands clutching at the back of his neck, until he removes them with a firm hand and puts them over your head.

“ya gonna be a good kitten tonight, or do i need ta get something to hold ya down?” he asks you lowly.

“I’ll be good, daddy,” you promise, and push your hands further into the sheets above your head, feeling yourself growing wetter at the feeling, so intoxicating every time, of giving yourself to him.

“good. don’ move a fuckin’ inch.” You do as he says, and he spreads your legs with firm hands, allowing him to see the moisture on your thighs and the glistening of your folds. He growls and breathes in deep. He’s leaning over you suddenly, pushing his face into your neck and smelling you, laving his tongue over your pulse point and teasing the skin with his teeth. “ya want my tongue, kitten?”

“Yes!” you say eagerly, nearly jerking your hands from their place above your head. He just chuckles and pulls back to watch you.

“yes, _what?_ ”

You subdue. “Yes, daddy. I want your tongue, please.”

He grins, teeth glinting, and looks at you with an unfathomable mixture of hard lust and soft desire. “where, baby?”

You duck your head despite yourself. “My cunt. Please, lick my cunt, daddy.”

“ya got it, sweetheart.”

He’s done this so many times, knows each fold of you so well, that he can make you cum in less than five minutes, and he puts every bit of his expertise to work, burying his face in you and moaning nearly as much as you do. The first time you had asked him why he likes eating you out so much, he said it was because you taste like mustard. The second time you asked him, after you had thrown a pillow at his shit-eating grin, he said it was because not even he can be lazy all the time. The third time you asked him, he said it was because there was nothing more intoxicating than watching you come undone and knowing that he had been the one to do it.

Honestly, the real reason was probably a mix of the three.

Regardless, he sucks your labia away from your body and circles your clit with his tongue with a distinctly drunk expression.

“yer _mine_ , kitten,” he mumbles into you, and there’s no possible way you could summon anything remotely like words right now, so you just moan long and loud in response, which just makes him increase his pace, and oh _fuck_ –

But you don’t cum, because you’re wearing the blue collar, and you _won’t_ , not until he removes one of his hands from its bruising grasp on your hip and shoves three fingers into you, not until he bites the inside of your thigh with viciously sharp teeth, not until you meet his eyes and see his teeth dripping with your juices. Not until he curls his fingers in you and shows you his tongue dripping with both him and you and snarls, “ _cum._ ”

You do.

It’s only after you can open your eyes again, what feels like a million years later, that you realize you’re holding his skull to your pussy with both hands. He could have removed himself easily, but he didn’t, and you know the reason why when you snatch your hands away and he takes his mouth off of you and just laughs.

“well, kitten, i’m flattered, but don’t ya remember the rules?”

“Yes, daddy, yes, I’m sorry I didn’t mean –“

“now, dollface. ya know i don’ give a shit about what ya meant. all i care about is what ya did. and what did ya do, kitten?”

You know this game. He won’t relent until you tell him. “I…. I moved my hands,” you say. “You told me not to move, b-but I did anyway. I-I was…” you have to swallow, this part is always the hardest, “I was a bad kitten.”

“an’ what do bad kittens get?”

“Bad kittens… bad kittens get tied up.”

“thaz’ right, baby. now ya stay right there, i’ll be right back.” He crosses the room and retrieves the set of silk scarves that are both of your favored restraints. You obligingly hold your limbs outstretched and still as he ties your hands to the bed frame.

He kisses you in the way that only he can, which is to say, he presses his teeth to your lips until you open your mouth. His tongue explores the roof of your mouth and the hollows of your cheeks, and even though you know you deserve to be tied up, you wish you could wrap your arms around him. Alas, it’s too soon when he pulls away, smirking a little at your petulant expression.

“don’ look like that, kitten. don’ ya want me ta fuck ya?” Yes, you do, so badly it almost hurts, your cunt aching to be stretched and filled. You nod your head emphatically, knowing he’s going to drag the spoken words out of you.

“beg me, you fuckin’ slut.” You shiver again and close your eyes for a moment at the degrading name. At your hesitation, he puts his hand around your neck, just above the firm press of your collar, and gives it a firm squeeze, cutting off your airflow for a moment before relaxing his grip. “ _beg._ ” His voice is almost a snarl now.

“Please, daddy, please fuck me, please use my cunt, I need it!”

He holds his cock with one hand, dragging it up and down your folds, pressing in the barest amount just to withdraw it and tease its fat head at your clit. You’re shaking in need, throwing your head back and making desperate noises. “dunno, baby, don’t seem like you really want it.” He keeps teasing you, squeezing your throat rhythmically, building you to the precipice of orgasm before squeezing your throat hard enough that you wheeze, holding his grip and bringing you back down with a deeply satisfied smirk. He knows being edged like this is torture, and you know how much he likes that fact as you watch his terrifying grin and blazing eyes through your tears. If your hands were free, you’d be rubbing your clit with one hand and pulling his cock into you with the other, consequences be damned, but restrained as you are all you can do is writhe against your bonds and try to breathe.

Oh god, you were going to explode, you wanted to cum so bad, you wanted his cock _so bad_ , but you didn’t know what else you could do to convince him. Unexpected tears rose to your eyes. You’re trying so hard to get the words out, but his hand around your throat makes it impossible. Finally, though, he deigns to notice your choked-off attempts to speak and loosens his grip, making you cough and gasp. Despite it all, you have to get the words out. “Daddy, daddy, daddypleaseIneedyoudaaaaddy –“ You break off into what sounds almost like a scream as he finally, _finally_ enters you, viciously hilting in one thrust and holding himself there as his teeth close on your shoulder. At first, you can’t even feel the pain, but when it hits, you wail, the feeling of his cock filling you so completely, the agony of his sharp teeth in you, the tightness of your collar, all combining to nearly overload your mind. You try to hold yourself back, but the sensations are so intense and the pain is so vivid and his cock is _so thick_ , and you can’t help it, you cum hard, back lifting off the mattress, mouth open wide in a silent scream, vision white. He holds you by the hips through all of it, teeth still locked in your shoulder.

When you finally come down, his skull is slick with sweat as he carefully removes his fangs from your flesh and grins at you. “that good, babe?”

“Yessssss….” You mumble, still unable to form proper words.

“ya want me to pull out?” Your eyes shoot open and you force your legs to lock around his pelvis. “No!” you nearly shout. True, you’re pretty damn sensitive, but the thought of being empty right now sounds much worse than a little overstimulation. “Just – just go slow, please?”

“sure thing, babe.” He pulls himself out of you, just a few inches, and back in, and you sigh gratefully as he sets up a smooth and slow rhythm. It seems he’s as unwilling to leave the embrace of your cunt as you’re unwilling to let him, and most of his cock stays deep inside you as he grinds against your clit with every thrust. You squeeze down on him as he pushes in on one particularly deep thrust, and his breath catches.

“ya belong ta me, yer _my_ lil’ pet – f - fuck –“ He’s kissing you again, and even though it’s still desperate and needy, it’s soft too, as he sucks on your tongue and sighs into your mouth, never ceasing the motion of his hips. He hooks two fingers in the hook of your collar, forcing your head up as he kisses you.

There’s no way you can cum again so soon, but the feeling of his cock pulling at your walls as you try and keep him from leaving, every ridge and bump striking nerves inside you, makes you keen softly. “Daddy – daddy – can you – my hands – wanna feel you –“ Your words are blurry and your mind is even worse, but he knows you and he knows what you need, and he reaches up to loosen your wrists without a word. As soon as they’re free you’re stroking all over him, his ribs, his vertebrae, pressing the back of his skull farther into your chest as he licks and bites at your nipples.

You can tell he’s getting close, as his thrusts increase slightly in intensity and his breath shudders out from his chest. “god, kitten –“

“I love you, I love you so mu-u-u-ch daddy,” you tell him, moaning thickly, and he gives a sob at that, his hips stutter into you one more time as he holds his cock inside you and cums. His hand is around your neck again, squeezing lightly as he groans, long and deep and loud. The magic that spurts from his cock is hot, and there’s so much of it, and you can feel it trickling back out of you, which saddens you a little. You want all of him, everything he will give you.

When his orgasm abates and he goes to pull out of you, you tighten your ankles around his pelvis and he smiles and says, “i love ya too, baby. but i gotta get ya cleaned up, so ya gotta let me go, ok?”

You don’t want to let him go, you want him to stay in you and never leave, but you know he’s right. You can feel the sting of the bite mark on your shoulder more acutely now, and you’re both sweaty and covered in each other, so you sigh and loosen your legs. He removes himself slowly, making you hiss at the pleasure-pain of your overstimulated cunt. He presses a finger to your entrance, watching his cum flow back out of you, but you cover his hand with your own. “Don’t,” you tell him. “I – I want it.” He looks almost bemused at that, but kisses you anyway, before rolling off the bed to pick you up. He carries you across the hall to your bathroom and sits you on the counter, making you shiver at how cold it is.

First things first, he removes your collar. This time, the time right after a scene, is the only time you don’t wear one, and your hands fly up to your neck unconsciously at the naked feeling. Removing the first aid kit from a drawer, he lays each item he’ll need out next to you. Finally, he turns the bath on and shakes a handful of bath salts into the steaming water. You watch the smooth motion of his bones as he bends and turns, moving quickly around the small room, and you don’t notice you’re shivering until he turns to you and frowns. “fuck, baby, you’re shaking. c’mere.” He gathers you in his arms and you go to lay your head on his shoulder automatically, but it’s not like a human’s shoulder and it doesn’t really work. You whine a little and he steps into the bath with you, settling you in his lap. You refuse to move, so he retrieves the soft sponge and gentle soap he always uses to clean you after a scene with a flick of a finger and a slight flare of his left eye, gathering water and soap before running it over your body. Despite yourself, you can feel the need coiling in your belly again, and you squirm a little on his legs.

He stills you with a hand on your thigh. “whaddaya need, kitten?” You’re not sure how to ask, so you reach your hand down and stroke his pubic bone. He chuckles a little. “again, babe?” You nod, and sigh happily when you feel his length materialize against the curve of your buttocks. He lifts you slightly, just enough to position himself, and then pulls you down again until he’s firmly nestled inside you.

Ah, that’s what you needed. Now you feel like you can really relax, and you do, eyes fluttering closed as he cleans you and fucks you simultaneously, so gentle in both actions that you feel almost like you could fall asleep. The little shocks of pleasure that run up your spine and the distinct feeling of fullness and safety that his magic gives you is so good you could cry if you weren’t so relaxed. You jolt a little when he touches the bite mark on your shoulder, but settle when his hand presses firmly on your chest.

You love giving yourself so totally to him during a scene. It satisfies something within you that you can’t get anywhere else, and makes you feel loved unconditionally. But you cherish this too, this gentle side of Sans that only you get to see. He cleans your shoulder wound with feather light touches, stroking your skin soothingly whenever the pain makes you tense a little. He’s focusing so hard that his cock has stilled completely within you, but you don’t mind, relishing the feeling of being so close. Finally, he finishes his careful work and sighs contentedly. “ya doin’ ok, baby?”

“Yeah,” you murmur. “Can you keep fucking me?”

He laughs a little, but starts up again, not even really thrusting in you so much as he rocks you both back and forth, grinding together in the water. He palms at your breasts, making you sigh in pleasure and reach down to play at your clit. When you cum, it’s nothing like the violent, overpowering climax of before. This orgasm rolls over you soothingly, like a wave, and you gasp and twitch around him. He curls his arm around your waist securely and fucks into you once – twice – and then he comes too, both of you whimpering at the feeling. He pulls out of you and you turn in the water to face him, wrapping your arms loosely around his neck and kissing him sloppily. He kisses you back, breathing hard into your mouth. You wouldn’t have even noticed him pulling the bath’s plug and lifting you easily from the water if not for the sudden chill on your lower body, but he fixes that almost immediately with a towel wrapped around your shoulders. He carries you back to your bedroom and sets you on your feet, and you dry each other haphazardly.

Eventually, you pull him down on to the bed, but sit up suddenly when you remember you still haven’t put your silver collar back on. “Babe – Sans, I need my collar,” you say, pulling at his collarbone. His eyes have already drifted shut, but he opens them lazily and looks at you with a distinctly disgruntled expression.

“do ya really need it, kitten?” he asks sleepily.

“Yes, Sans,” you say firmly, and he groans and rolls out of bed. He fastens the thin chain around your neck with a strange expression. “What are you thinking about, bonehead?” you ask him curiously.

“i was tryin’ to come up with a joke about _fetching_ your collar for you. ya know, cuz dogs and collars? fetch?” The honesty and _Sans-_ ness of his answer surprises you, and you laugh louder than it probably warrants. He raises a supraorbital ridge at you and you giggle helplessly. “whaddaya laughin’ about, sweetheart?” he asks, faux-puzzled.

“I love you,” you say emphatically, and he grins and says, “yeah, i figured.”

You punch him lightly in the arm, more for the sake of your hand than any consideration on whether it’ll hurt him (it won’t) and lean over to kiss his cheek. “Let’s go to sleep, babe,” you say, and he looks positively elated at the prospect, pulling you down and spooning you, dragging the blankets over you with a lazy gesture of one finger.

He reaches a hand over you to hold the silver clasp of your collar, and you push yourself farther back, into his skeletal body. It’s hard, full of ridges and bumps and uncomfortable sharp spots, but you don’t care. You’re warm, drowsy, and contented. “love you too,” you hear him mumble at the edges of your consciousness, and you drift into sleep with a smile on your lips.

**Author's Note:**

> [tumblr](https://syzygykitty.tumblr.com/)


End file.
